The present invention relates to a power tool of the type which is adapted to hold an inserted tool bit which can be operated with a rotating action and a hammer action, hammer means of which tool can be activated by axial displacement due to the engagement of the inserted tool bit with the work piece to be worked upon. Such tools may comprise a manually operable adjustment handle which can be rotated about an adjustment axis between a first position in which a stop element permits axial displacement for the activation of the hammer means, and a second position in which the stop element blocks the axial displacement, and the invention relates to improvements in switching such a tool from one mode of the operation to another.
An electric power tool of this type in the form of a rotary hammer is described in European Patent No. 0 331 619. In this rotary hammer the adjustment handle has a rotary knob mounted in the casing wall, to which a pin which extends into the inner space of the casing is eccentrically connected, which in one position permits the axial displacement for the activation of the hammer mechanism so that the rotary hammer operates in the combined drilling and hammer mode, while in the other position, rotated about the adjustment axis opposite the first position, it lies against a disk which sits on the spindle of the rotary hammer and which can be moved together with the latter, and thus prevents the displacement of the spindle by the engagement of the inserted tool bit with the work piece and therefore prevents the activation of the hammer mechanism so that the rotary hammer operates in the pure drilling mode while the coupling for linking the hammer-mechanism to the rotary-driven intermediate shaft which rotatably drives the spindle is not engaged.
In this known electric power tool, it is therefore possible to switch between two modes of operation, namely combined drilling and hammering on the one hand, and pure drilling on the other. Frequently, however, it is also desirable to be able to switch into a further mode of operation, for example when in the pure drilling mode to switch from drilling at low speed to drilling at a higher speed. To achieve this in another known rotary hammer (German Patent Application P 34 45 577.9) two separate adjustment handles are provided, one to activate and deactivate the hammer mechanism, the other to enable switching between different speeds. In this arrangement with two adjustment handles each specific to different functions, in order to avoid switching to non-permitted combinations of operational modes, such as activation of the hammer mechanism at high speed, the adjustment handles are arranged directly beside one another with their grip sections constructed such that the adjustment handle for the hammer mechanism cannot be rotated into the position for the activation of the hammer mechanism when the adjustment handle for the speed is in the high-speed position. As a result, however, the construction is relatively complicated because not only are two separate adjustment handles required, but these must be provided in a quite specific way and in close spatial co-ordination on the electric power tool, which not only results in an expensive construction but also creates limitations as to the design of the interior structure of the electric power tool.
The object of the invention is to provide a power tool having a switching device with a simple construction which makes it possible to switch between at least three modes of operation without the risk of an incorrect combination.